Another way to do this is to put everyone in a chain, and have each person be listening to what the person before them was playing a few seconds ago. I wrote some software that does this, and anyone is welcome to play with it: https://echo.jefftk.com

It's open source: https://github.com/gwillen/solstice-audio-test

Here's an example with some informal singing my friends and I were doing this evening: https://echo.jefftk.com/recordings/2021-01-15-023012.wav (it makes ephemeral recordings)

Not the same as your idea, but similar is NINJAM, which is tempo synced, but deliberately makes the latency equal to one bar, phrase, or other segment of time. You are always playing live to what everyone else played the very last time around, but you are still playing on the beat together. It obviously works better for repetitive jam sessions than for structured songs, but it looks very interesting. I haven't yet tried it with my music buddies, and should.

[1] https://www.cockos.com/ninjam/

Bit unrelated, but I recall an old webpage that had a grid of 10 or so YouTube videos embedded, each with a different instrument playing (they didn’t auto play).

This was pre-mobile, so it was expected that you could play multiple videos at once. I was amazed, and it was the intent, that independent of how few or many videos you played and no matter when you started each of them, all sounds blended together nicely.

I don’t know what to call it when there’s no inter-sound coordination - a timing independent harmony? It was so cool.

Anyways, I would be super interested in attending a zoom concept of that sort that might side step some technical difficulties.

This is correct. The reason is more or less that humans are really, really good at staying in sync, but, even with only 2 parts to listen to, it starts to get almost impossible levels of effort to keep proper time. In person, without any network lag, musicians can make adjustments in real time (e.g. always, always, always follow the soloist, even if the soloist is off tempo or off pitch). The conductor is listening to the soloist, too, so you don't need to worry about conflicting directions.

Here are a couple of examples I know of on YouTube where a single musician plays multiple parts, which are then edited together:

Now professional cellist, graduating senior at time of recording, Sarah Chaffee playing an original transcription of Alice Cooper's Poison with 5 cello parts (with a short guest appearance by Shostakovich at about 2:42, then showing up again in the outro to play us out at 3:33): https://www.youtube.com/watch?v=PjYwQHFsld0

Professional cellist Wells Cunningham playing the Handel- Halvorsen Passacaglia: https://www.youtube.com/watch?v=NseBdxfHk5k

This guy has a really, uhm, interesting violin technique. ;) Just for the fact that he chose to play the instrument the way he did tells me he does not actually know how to play violin. What he's doing is playing it like a teeny tiny cello. Since the notes are so much closer together on the respective fingerboards on a violin than on the cello, I'm betting he needed an extra take or 2 on that. His performance is passable, but nothing when put up against the performance of an actual, professional violinist.

Zoom is not the right software for this. It already exists. There are many online streaming musical collaboration tools, including free ones. Jamkazam is one example.

My band did that for a while. It was a lot of work for the producers.

We also played a specially composed piece for playing over zoom. We each recorded separately then sent our files in later. But it was live. And the music was super-simple.